So you're saying oversaturation would be an issue when the market becomes oversaturated. Got it

Ha ha.

There's two different usages of the term "over-saturation," here. One is the idea of "superhero fatigue", that people will get "tired" of superhero movies if there are too many of them. I see no evidence that this is actually a meaningful problem. The other is that if you have too many superhero movies, you'll run out of release dates. This is true, but its also not a problem for Marvel Studios so much as for the entire movie industry. Superhero movies compete for good release dates with all other demographically-similar movies; a big budget sci-fi or action movie is just as much competition for release dates as another superhero movie would be.